GNU bug report logs - #347
C mode asks twice about local variables

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From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Alan Mackenzie <acm <at> muc.de>
Cc: Glenn Morris <rgm <at> gnu.org>, 347 <at> debbugs.gnu.org,
        bug-cc-mode <at> gnu.org, bug-gnu-emacs <at> gnu.org
Subject: bug#347: C mode asks twice about local variables
Date: Mon, 09 Jun 2008 11:18:28 -0400

>> > Yes.  This needs fixing, somehow.
>> 
>> > The way this happens is that in a C file's local variables list, there
>> > are two "special" variables, e.g. `c-file-style'.
>> 
>> > When 
>> 
>> >     c-basic-offset: 11
>> >     c-file-style: "k&r"
>> 
>> > occurs in the local variable list, this triggers a hook function
>> > which calls (c-set-style "k&r").  The hook is
>> > hack-local-variables-hook.  The problem is that this c-set-style call
>> > will overwrite the explicit value for c-basic-offset.  The explicit
>> > value MUST take precedence here.
 
>> Can you try and call `c-file-style' with some extra "don't override"
>> (when called from that hack-local-variables-hook) argument so that any
>> variable that already has a buffer-local binding will not be
>> overridden?

Any comment about this suggestion?

>> > My solution was to call hack-local-variables a second time from
>> > within the hook function, first having deleted any occurrences of
>> > `mode', `c-file-style' etc. from the Local Variables.  This kludge
>> > worked reasonably well until the handling of
>> > safe/dangerous-local-variables was changed for Emacs 22.

>> How 'bout wrapping the call inside (let ((enable-local-variables
>> :safe))?

> I've been thinking this over.  It's not the right solution.  For a start,
> the second call to `hack-local-variables' is in itself a kludge.

I'd tend to agree, but "kludge" fixes the problem, it's still better
than the current "same kludge + problem".

> More importantly, the value ":safe" is non-portable (to earlier Emacsen,
> or to the other one),

Non-portability might indeed be a problem (tho, it's obviously "your"
problem rather than mine), but introducing a new hook in Emacs-23 won't
help you there, so it's not relevant to this discussion.

> and doesn't feel at all safe.

But I don't see why you don't consider it safe: it is really meant to be
safe, so if there's any doubt about it, we should very much address it.

> (defvar before-hack-local-variables-hook nil
[...]
> What do you think?

I'm not thrilled.  You might convince me at some point, but the kludge
doesn't look nearly as bad when compared to this hook.


        Stefan

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